Ruslan Ivanov

Highly polarized photoluminescence and its dynamics in semipolar (202¯1¯) InGaN/GaN quantum well

Very high polarization degree of 0.98, considerably larger than theoretical predictions, has been measured in (202¯1¯) In0.24Ga0.76N/GaN quantum well by low temperature photoluminescence. With increasing temperature, the polarization degree decreases due to thermal population of the excited valence band level. This effect suggests an accurate method to determine the interlevel energy, which, for the studied well, is 32 meV. Time-resolved photoluminescence measurements set radiative recombination times between 2 and 12 ns for temperatures from 3 to 300 K. Nonradiative recombination was found to be slow, over 2 ns at 300 K, taking place via traps with activation energy of 0.19 eV.

High spatial uniformity of photoluminescence spectra in semipolar (202¯1) plane InGaN/GaN quantum wells

Scanning near-field optical spectroscopy was applied to study spatial variations of emission spectra at room temperature in semipolar (20 (2) over bar1) InxGa(1-x)N/GaN single quantum wells (QWs) f ...

Impact of carrier localization on radiative recombination times in semipolar (202¯1) plane InGaN/GaN quantum wells

Semipolar (20 (2) over bar1) plane In,Ga1-xN quantum wells (QWs) of varying alloy composition were studied by time-resolved photoluminescence. A large difference in effective radiative lifetimes. f ...

Scanning near-field microscopy of carrier lifetimes in m-plane InGaN quantum wells

Time-resolved scanning near-field photoluminescence (PL) spectroscopy was applied to map carrier lifetimes in wide m-plane InGaN/GaN quantum wells grown on on-axis and miscut substrates. Both radiative and nonradiative lifetimes were found to be spatially nonuniform. Lifetime variations were smaller for quantum wells grown on miscut, as compared to on-axis substrates. Correlation with surface topography showed that largest deviations of recombination times occur at +c planes of pyramidal hillocks of the on-axis sample. Observed correlation between radiative lifetimes and PL peak wavelength was assigned to a partial electron localization.

Properties of near-field photoluminescence in green emitting single and multiple semipolar (202¯1) plane InGaN/GaN quantum wells

Scanning near-field photoluminescence (PL) spectroscopy has been applied to green emitting (202¯1) plane InGaN/GaN quantum well (QW) structures with 1, 5 and 10 wells to reveal the influence of the number of QWs on PL properties and their spatial variation. The data show no additional broadening or shift of the PL spectra related to the increase of the number of QWs. The QWs in the multiple QW structures are found to be nearly identical and the well width and/or alloy composition fluctuations uncorrelated. In spite that the thickness of the 10 QW structure is over the critical, no PL changes related to a structural relaxation have been detected.

Impact of alloy composition and well width fluctuations on linewidth broadening and carrier lifetimes in semipolar InGaN quantum wells (Conference Presentation)

Band potential fluctuations in InGaN/GaN quantum wells (QWs) induce carrier localization that affects emission linewidth and carrier recombination rate. Alloy composition and well width variations are considered as main sources of the potential fluctuations and are often treated indiscriminately. However, their impact on the emission linewidth and the carrier lifetimes may be different. Besides, the impact of the QW width fluctuations on the linewidth could possibly be reduced via optimization of growth, while random alloy composition fluctuations can hardly be avoided. In this work, we have studied these effects in green-emitting semipolar (20-21) plane InGaN/GaN single QW structures of different well widths (2, 4 and 6 nm) and in structures with different number of QWs (1, 5 and 10). Experiments have been performed by scanning near-field photoluminescence (PL) spectroscopy. It has been found that the well width fluctuations, compared to the InGaN alloy composition variations, play a negligible role in defining the PL linewidth. In multiple QW structures, the alloy composition fluctuations are spatially uncorrelated between the wells. Despite that the 10 QW structure exceeds the critical thickness, no PL linewidth changes related to a structural relaxation have been detected. On the other hand, the well width fluctuations have a large impact on the recombination times. In-plane electric fields, caused by the nonplanarity of QW interfaces, separate electrons and holes into different potential minima increasing the lifetimes in wide QWs.

Influence of well width fluctuations on recombination properties in semipolar InGaN quantum wells studied by time- and spatially-resolved near-field photoluminescence

Scanning near-field photoluminescence spectroscopy has been applied to distinguish the relevance of quantum well (QW) alloy composition and well width fluctuations on emission linewidth and recombination times in semipolar (202¯1) plane InGaN QWs. It has been found that well width fluctuations, compared to variations of InGaN alloy composition, play a negligible role in defining the photoluminescence linewidth. However, the well width strongly affects the recombination times. Prolonged radiative and nonradiative carrier lifetimes in wide QWs have been attributed to electron and hole separation by in-plane electric fields caused by nonplanarity of QW interfaces.

Spatial variations of optical properties of semipolar InGaN quantum wells

Spatial variations of band potentials and properties of carrier recombination were examined in semipolar (2021) plane InGaN/GaN single quantum wells by scanning near-field photoluminescence (PL) spectroscopy. The quantum wells had In content from 0.11 to 0.36 and were emitting from violet to yellow-green. Near-field scans showed small PL peak energy and linewidth variations with standard deviations below 10 meV, which confirms small alloy composition variations in the quantum wells. The scans revealed large, ~5 to 10 μm size areas of similar PL parameter values, as opposed to 100 nm scale variations, often reported for InGaN wells. With increased excitation power, an untypical photoluminescence peak energy shift to lower energies was observed. The shift was attributed to density dependent carrier redistribution between nm-scale sites of different potentials. The experimental results show that in the (2021) plane InGaN quantum wells the localization potentials are shallow and the recombination properties are spatially rather uniform, which confirms the high potential of these QWs for photonic applications.